Thanks, so it definitely appears to be a much more sophisticated attack than what occurred in Atlanta.
Agree. That was a single device with a timer. This has at least 3 bombs, and while may have had a timer, was evidently timed to involve a lot of runners (not the first few winners - often spread out a lot) and a lot of spectators. You could argue that more Americans would have been expected to be finishing the race at this time, too, as opposed to the international participants. But that speaks to the bomber's motivation, which we'll have to wait on.
I will add that routine security inspections should have checked trash cans, so I'd be checking area footage over the past 3-4 hours to see if these things weren't planted in that time period.